Recent progress in digital image processing technique and flat panel display devices (FPD) makes it possible to realize high-quality images with ultra-high-resolution. A Liquid Crystal Display (LCD) panel is composed of vertical and horizontal array of pixels. Each pixel is selected by a row driver and the light transmission, therefore the brightness, for the selected pixel is determined by the voltage level which is controlled by a column driver.
The column driver drives a multiple number of pixels, for instance, sixteen (16) pixels in the exemplary case shown in FIG. 1, which inevitably produces an offset voltage among the output channels. The inter-channel offset voltage causes the offset in voltages which are applied to data lines of each pixel, which results in a noticeable vertical stripe artifacts and degradation of image quality. The vertical strip artifacts become more discernable particularly in a small-size screen device such as a micro display device.
A variety of technical solutions have been proposed in an effort to resolve the inter-channel offset voltage problem. For example, the prior art discloses a technique where the size of a transistor at the input is increased for the compensation of the inter-channel offset voltage. Much effort has been made in the tight control of the semiconductor chip manufacturing process in order to prevent the generation of the offset.
However, the prior art of controlling the size of the input transistor has a technical limit because the chip size and therefore the manufacturing cost also increases with the size of the transistor. Furthermore, it is inevitable to have some variations and fluctuations in the production line despite of the tight control of a semiconductor chip manufacturing process. Moreover, the offset which is produced during the digital-analog converting process is also unavoidable as well as in the amplifiers. More recently, an approach was proposed wherein an offset voltage for each channel is detected via Analog-to-Digital Converters (ADC) for controlling the bias value of an amplifier (AMP) and the offset is subtracted from input digital data in order to compensate for the detected offset voltage.
This method, however, also has a shortcoming in that the ADC itself connected to each channel possibly has its own offset characteristics and therefore additional offsets can be generated due to the inherent offsets present in the ADC which was used for the compensating purpose of channel offset. In other words, the prior art has a technical limit because of the inherent presence of the offsets among the ADCs which are connected to the channels, which has to be removed in the design of the offset-removing ADCs.